The present invention relates generally to indoor air quality measurement, and more specifically to devices for monitoring the temperature and quality of air in building environments.
Indoor air quality (IAQ) has become an important consideration in creating a satisfactory environment for today's building occupants, particularly in office buildings, schools, and health care facilities. Indoor air quality is a constantly changing interaction of a complex set of factors, which must be considered when looking for an indoor air quality problem. These factors include the source of contamination or discomfort; the heating, ventilating and air conditioning (HVAC) system not being able to control existing air contaminants and ensure thermal comfort; pollutant pathways connecting the pollutant source to the occupants with a driving force existing to move pollutants along the pathways; and the building occupants that are affected by the indoor air quality.
Indoor air contaminants can originate within the building or be drawn in from outdoors. One technique for controlling odors and contaminants is to dilute them with outdoor air. However, dilution can only work if there is a consistent flow of supply air that effectively mixes with the room air. Air flow patterns in buildings result from the combined action of mechanical ventilation systems, human activity and natural forces. Pressure differentials created by these forces move airborne contaminants from areas of relatively higher pressures, to areas of relatively lower pressure through any available openings. All of a building's walls, ceilings, floors, HVAC equipment and occupants interact to affect the distribution of contaminants. Since different people have different sensitivities to contaminants, one individual may react to a particular IAQ problem differently than surrounding occupants. The effects of indoor air quality problems are often non-specific symptoms, rather than clearly defined illnesses. The air quality in commercial buildings such as office complexes and educational institutions is primarily controlled by thermostats. The thermostats are distributed within the workspace and are used to control Variable Air Volume (VAV) boxes or other aspects of the building HVAC system. The HVAC system includes all heating, cooling, and ventilation equipment that serves a building. This includes furnaces or boilers, chillers, cooling towers, air handling units, exhaust fans, ductwork, filters, and piping. HVAC systems maintain air quality by mixing fresh outdoor air with the indoor air. VAV systems work on the principle that space temperature can be maintained by varying the volume of air delivered to a space as the load changes. As the load decreases in the space, the VAV system throttles the air flow to match the space requirements. As the VAV terminal box opens and closes, the static pressure in the ducting increases and decreases. The change in pressure is sensed by the VAV controller which reacts to vary the air delivered by the unit. In this application, HVAC and VAV systems will be referred to generally as building energy management systems.
Both the American Society of Heating, Refrigeration, and Air Conditioning Engineers (ASHRAE) and OSHA have established rules for proper ventilation. OSHA estimates that the excess risk of developing the type of non-migraine headache that may require medical attention or restrict activity, which has been associated with poor indoor air quality, is 57 per 1000 exposed employees. In addition, the excess risk of developing upper respiratory infections that are severe enough to require medical attention or restrict activity is estimated to be 85 per 1000 exposed employees. These numbers were extrapolated from actual field studies and therefore show the magnitude of the present problem. ASHRAE has specified minimums for ventilation rates and indoor air quality that will be acceptable to occupants. These requirements are published in ASHRAE Standard 62-1989.
The maximum amount of ventilation provided by an HVAC system may be limited, not only by the system's capacity, but also by the temperature and humidity of the outside air. Uniformity of temperature is important to individual comfort. Humidity is also a factor in thermal comfort. Raising relative humidity reduces the ability to lose heat through perspiration and evaporation, so that the effect is similar to raising the temperature. Since the outdoor air may be substantially hotter or colder than the specified indoor air temperature, the HVAC system must work harder to reach the specified temperature set point. This results in inefficient use of building energy and waste. However, temperature alone is not a sufficient indicator of indoor air quality. The level of personal comfort is closely related to other gases in the atmosphere. New building construction techniques and materials significantly aggravate air quality problems because of the out gassing of undesirable substances, such as Volatile Organic Compounds (VOCs). VOCs include carbon dioxide (CO2), carbon monoxide (CO), formaldehyde, and other compounds. CO2 sensors can be used in addition to temperature sensors (i.e., thermostats), but CO2 sensors are expensive and therefore are used very infrequently. When they are used, they tend to be located in the return plenum or in the ducts. This technique frequently combines return air from several occupied spaces and gives no direct indication of the quality of the air in a specified space. An inexpensive sensor system is needed that accurately represents room conditions, yet is in the air stream to the return air plenum.
Most pollution sensor devices are expensive laboratory equipment or stationary wall or ceiling mounted systems. Commercial and residential units typically monitor only one variable. In addition to the need for multiple sensor devices located in the return air flow, what is also needed is a multiple sensor device that is mobile and can have its data downloaded in real-time to a system or network from which the air flow temperature and mix can be controlled. The mobility of a hand-held pollution tester allows for the testing of various spaces in a building that can be overlooked by the placement of stationary devices. For example, during new construction, it is easy to monitor the contribution of each new building component, such as carpets and ceiling tiles, to the indoor environment. Therefore, what is needed is a portable device that can be used where existing sensor systems are inadequate, out-of-date, or lacking specific sensors.
In the prior art, U.S. Pat. No. 6,125,710 to Sharp discloses a networked air measurement system that includes a sensor for measuring a characteristic of an air sample, the sensor having an inlet port, a backbone tube in communication with the air inlet port of the sensor, a plurality of air intake valves in communication with the backbone tube with air admitted through one of the plurality of air intake valves communicated into the backbone tube. The system further includes an air flow induction device that is in communication with air in the system, air being moved by the air flow induction device from the plurality of air intake valves, through the backbone tube to the sensor. A controller is connected to the sensor and to each air intake valve and executes a control sequence, which opens and closes air intake valves to admit air and form air samples that are communicated to the sensor. The controller uses time intervals or air sample measurements to determine the appropriate times at which to open individual air intake valves.
Also in the prior art, U.S. Pat. No. 6,111,501 to Honeyager, et al. discloses a hand-held environmental monitor for monitoring environmental or physiological conditions affecting the user. The monitor includes a main housing and a sensor module. The sensor module has a plurality of sensors extending from it. The sensor module is generally cylindrical in shape and rests in a curved cradle of the main housing. The sensor module rotates between a position in which the sensors are deployed and extend outwardly from the main housing, and a position in which the sensors rest in the main housing. The main housing also contains processor-based electronics circuitry for processing the data acquired by the sensors. The sensor module contains sensor electronics circuitry, including all circuitry that is unique to the sensors, and is detachable from the main housing. This permits sensor modules having the same or different sensors to be interchanged.